This will allow 5 concurrent moves from the source database, 2 concurrent moves to the target database, 50 per sources server, 5 per target server and 100 per CAS server. If you use high-end disk with plenty of IOPS, you can change the settings gradually up to something like this (be aware of your hardware limitations):

This will require a restart of the MRS service on the CAS server(s). You can edit these settings in the file MSExchangeMailboxReplication.exe.config, wich would normally exist on the CAS server in C:\Program Files\Microsoft\Exchange Server\V14\Bin\. For more details read this TechNet article.